AbstractFractionation of barbados cherry (acerola fruit, a fruit of Malpighia emarginata DC.) extracts were performed by organic solvent extractions and column chromatographies, using two extraction methods. Higher cytotoxic activity was concentrated in fractions A4 and A6 (acetone extract), and H3 and HE3 (hexane extract). These four fractions showed higher cytotoxic activity against tumor cell lines such as human oral squamous cell carcinoma (HSC‐2) and human submandibular gland carcinoma (HSG), when compared with that against normal cells such as human periodontal ligament fibroblasts (HPLF) and human gingival fibroblasts (HGF). HE2 (hexane extract), AE2 (ethyl acetate extract), AE3, AE4, AE5, A8, A9 and A10 showed some relatively higher anti‐bacterial activity on the Gram‐positive Staphylococcus epidermidis ATCC 1228 but were ineffective on the representative Gram‐negative species E. coli and Ps. aeruginosa. The fractions were inactive against Helicobacter pylori, two representative Candida species, and human immunodeficiency virus (HIV). H3, H4 and HE3, which displayed higher tumor‐specific cytotoxicity also showed higher multidrug resistance (MDR) reversal activity, than (±)‐verapamil as positive control. ESR spectroscopy shows that the radical‐mediated oxidation is not involved in the induction of tumor‐specific cytotoxic activity. The tumor specific cytotoxic activity and MDR reversal activity of barbados cherry may suggest its possible application for cancer therapy. Copyright © 2004 John Wiley & Sons, Ltd.